Richard Fairhurst wrote: >Sent: 24 January 2008 3:52 PM >To: [email protected] >Subject: Re: [OSM-talk] Mapping canals > >Andy Allan wrote: > >> 2) There are two different things that everyone is talking about, and >> keep getting them confused >> * The distance, or speed, that you are recording (i.e. the physical >> property). Units are interchangable, can be converted etc to your >> heart's content. >> * The manner in which the measurement is displayed in the real world >> (i.e. the evidence, signs etc) > >And a third, which might sound obscure but is actually a big issue >when we get back to canals: > > * The specification of the measurement > >A UK narrow lock is 7ft wide. It isn't 2.14m wide. > >It sounds like nit-picking, but I've just typed "2.14" in because I'd >memorised that as narrowboat-width-in-metres and that's what some of >the brokers put in their ads. > >If you quote 7ft to 2 significant figures, it's 7ft. If you quote >2.14m to 2 significant figures, it's 2.1m. There are narrowboats out >there which will get through a 2.14m lock but not a 2.1m lock. There >are locks (on the Chesterfield Canal) which have actually been >built/restored too narrow because of measurement-cluelessness on the >part of the contractors. It does happen. > >(Actually, on checking with a calculator, 7*12*2.54=213.36. So I'm >doing a bit of unconscious rounding already.) >
Indeed, the exact conversion is to multiply/divide by 0.3058 which produces 2.1336m or 2.134m if you round to the nearest millimetre. 7ft or 7' is so much simpler in this instance :-) >Whether or not the maxwidth tag accepts measurements in feet is >probably something that'll eventually be decided by renderer, routing >app and editor authors, but there is certainly a need for the "7ft" to >be recordable in the db. > Cheers Andy _______________________________________________ talk mailing list [email protected] http://lists.openstreetmap.org/cgi-bin/mailman/listinfo/talk
